1. Field of the Invention
The present invention relates to an apparatus for detecting the remaining capacity of a battery, and more particularly to a remaining battery capacity detecting apparatus for use on an electric vehicle that is propelled by electric energy supplied from a battery as an energy source.
2. Description of the Related Art
Apparatus which use a battery as an energy source, e.g., electric vehicles or the like, often need to recognize the remaining capacity, expressed in ampere-hours (Ah), of the battery.
Heretofore, it has been customary practice to calculate the remaining capacity of a battery by correcting the fully charged capacity of the battery, i.e., an initial capacity (a calculated value or a fixed value based on battery standards, also referred to as a rated capacity) according to the following equations (1)-(3): EQU Remaining capacity=initial capacity-integrated discharging current (when the battery is discharged) (1) EQU Remaining capacity=initial capacity+integrated charging current (when the battery is charged) (2) EQU Remaining capacity=previously detected remaining capacity-estimated self-discharged quantity (when the battery is left to stand)(3)
Basically, as can be seen from the equation (1) or (2), an initial capacity is obtained when the battery is charged to its full capacity, and then charging and discharging currents flowing into and out of the battery are detected by a current sensor. The initial capacity is corrected by an integrated value of the charging and discharging currents for thereby recognizing the remaining capacity of the battery at present.
However, the current sensor for detecting charging and discharging currents flowing into and out of the battery suffers a relatively large error. Therefore, when the battery is charged and discharged in repeated cycles without being fully charged, current sensor errors are accumulated, resulting in a reduction in the accuracy with which the remaining capacity is detected.